Most calculus students are familiar with the calculus problem of finding the optimal path from A to B. “Optimal” may mean, for example, minimizing the time of travel, and typically the available paths must transverse two different mediums, involving different rates of speed.
This problem comes to mind whenever I take my Welsh Corgi, Elvis, for an outing to Lake Michigan to play fetch with his favorite tennis ball. Standing on the water’s edge (See Figure 1) at A, I throw the ball into the water to B. By the look in Elvis’s eyes and his elevated excitement level, it seems clear that his objective is to retrieve it as quickly as possible rather than, say, to minimize his expenditure of energy. Thus I assume that he unconsciously attempts to find a path that minimizes the retrieval time.